There are high expectations regarding utilization of pattern transfer techniques that employ a nanoimprinting method to transfer patterns onto resist coated on objects to be processed, in applications to produce magnetic recording media such as DTM (Discrete Track Media) and BPM (Bit Patterned Media) and semiconductor devices.
The nanoimprinting method is a development of the well known embossing technique employed to produce optical discs. In the nanoimprinting method, an original mold (commonly referred to as a stamper or a template), on which a pattern of protrusions and recesses is formed, is pressed against resist coated on an object to be processed. Pressing of the original onto the resist causes the resist to mechanically deform or to flow, to precisely transfer the fine pattern. If a mold is produced once, nano level fine structures can be repeatedly molded in a simple manner. Therefore, the nanoimprinting method is an economical transfer technique that produces very little harmful waste and discharge. Therefore, there are high expectations with regard to application of the nanoimprinting method in various fields.
In the conventional nanoimprinting method, an object to be processed was uniformly coated with resist by the spin coat method or the like, to form a resist film thereon. Thereafter, the surface of the mold having the pattern of protrusions and recesses thereon is pressed against the resist film, to perform pattern transfer. However, when pattern transfer is performed in this manner, there are cases in which fluctuations occur in the thickness of a residual layer (residual resist film which is not pressed during imprint molding, and remains at positions corresponding to the protrusions of the pattern of protrusions and recesses of the mold; also referred to as “residue”) of the resist film on which the pattern has been transferred. In such cases, the residual layer is generally removed by dry etching with settings that enable the thickest residual layer to be removed. During such removal, problems occur, such as the base layer underneath thin portions of the residual layer being etched as well, and protrusion portions of the pattern which should remain as a mask are excessively etched, which result in the processing accuracy of a substrate deteriorating. This is considered to be due to the fact that the pressing force applied by the upper surfaces (the surfaces that face the resist film during imprinting) of protrusions having large areas and the pressing force applied by the upper surfaces of protrusions having small areas are different. Another factor is that the resist is coated uniformly, although patterns of protrusions and recesses have protrusions or recesses of difference widths by nature, and the coarse and fine recesses act as escape routes for the resist when the patterns are pressed against the resist.
In view of the above, PCT Japanese Publication No. 2008-502157, and U.S. Patent Application Publication Nos. 20090014917, 20090115110, 20070228593, and 20090148619 disclose methods that employ the ink jet method to control the amount of resist to be coated at each region of objects to be processed, according to the pattern density (the percentage of protrusions or recesses per unit area when a pattern of protrusions and recesses is viewed from above) of patterns of protrusions and recesses when molds are pressed against the objects to be processed. That is, the publications listed above employ the ink jet method to reduce fluctuations in thickness of the residual layer, by optimizing the positional distribution (droplet arrangement pattern) at which droplets of resist material are arranged on objects to be processed according to pattern densities.
In addition, Japanese Unexamined Patent Publication No. 2008-042187 discloses a method for adjusting the amount of droplets and coating orders, to solve the problem that evaporation times of components differ due to temporal differences among timings at which droplets are coated.
However, the methods disclosed in the publications listed above assume the droplets spread isotropically when the mold is pressed against the droplets, and define the droplet arrangements such that spaces among adjacent droplets are minimal. Therefore, problems of thickness fluctuations in the thicknesses of residual layers and defects due to residual gas persist, in regions of the patterns of protrusions and recesses where patterns are formed as lines.
The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to provide a nanoimprinting method that suppresses fluctuations in thickness of a residual layer and defects due to residual gas in a resist film, onto which a pattern of protrusions and recesses is transferred, in a nanoimprinting method that employs the ink jet method to coat a substrate with droplets of resist material.
It is another object of the present invention to provide a method for producing a droplet arrangement pattern to be utilized in a nanoimprinting method that employs the ink jet method to coat a substrate with droplets of resist material that enables fluctuations in thickness of a residual layer and defects due to residual gas in a resist film, onto which a pattern of protrusions and recesses is transferred, to be suppressed.
It is still another object of the present invention to provide a method for fabricating substrates that enables highly accurate and high yield fabrication of substrates, by suppressing fluctuations in thickness of a residual layer and defects due to residual gas in a resist film, onto which a pattern of protrusions and recesses is transferred.